Radiographic images captured using films have been widely used heretofore in medical settings. However, since a radiographic image captured using a film provides analog image information, in recent years, digital radiographic image detectors such as computed radiography (CR) and flat panel radiation detectors (flat panel detector: FPD) have been developed.
The FPDs include a direct system FPD and an indirect system FPD. In the indirect system FPD, a scintillator panel is used for converting a radiation into visible light. The scintillator panel includes, as a constituent element, a phosphor layer containing a phosphor such as cesium iodide (CsI) or gadolinium oxysulfide (GOS). The phosphor emits visible light in response to an applied radiation, and the emitted light is converted into electric signals by a TFT or a CCD. In this way, radiographic information is converted into digital image information.
As a method of forming a phosphor layer, a method in which a coating film of a paste-like phosphor powder is used as a phosphor layer is simple; however, the light emitted from a phosphor is scattered within the coating film, and image clarity is extremely low. Therefore, in order to utilize light emitted from a phosphor with high efficiency by suppressing scattering of the emitted light, there are proposed, for example, a method of alternately arranging a phosphor layer formed of a phosphor of a large particle diameter and a phosphor layer formed of a phosphor of a small particle diameter (Patent Document 1), a method of disposing a barrier rib for dividing the phosphor layer (Patent Documents 2 to 4), and a method of improving an S/N ratio by forming a phosphor having a columnar crystal structure such as CsI by means of vapor deposition and guiding the light emitted from a phosphor to a TFT or a CCD (Patent Documents 5 to 6).